1. Field of the Invention
The present invention relates to a signal line and the circuit substrate thereof, and, more specifically, relates to a signal line that is capable of being easily inflected and reducing unnecessary radiation, and a circuit substrate thereof.
2. Description of the Related Art
As a signal line of the related art, for example, a flexible substrate described in Japanese Unexamined Patent Application Publication No. 2007-123740 is known. FIGS. 5A and 5B are cross-section structure diagrams of a flexible substrate 500 described in Japanese Unexamined Patent Application Publication No. 2007-123740.
A cross-section structure illustrated in FIG. 5A and a cross-section structure illustrated in FIG. 5B are alternately disposed, and hence the flexible substrate 500 is configured. More specifically, the flexible substrate 500 includes insulation layers 502a to 502d, a signal line 504 and ground layers 506a and 506b. Insulation layers 502a to 502d are sheets including flexible material and laminated. The signal line 504 is provided on the insulation layer 502c, and extends parallel to the vertical direction of the plane of paper of FIG. 5A.
As illustrated in FIG. 5A, the ground layer 506a is provided on the insulation layer 502b, and located above the signal line 504 in a lamination direction. As illustrated in FIG. 5A, the ground layer 506b is provided on the insulation layer 502d, and located below the signal line 504 in the lamination direction. In this way, in the flexible substrate 500, in the cross-section structure diagram illustrated in FIG. 5A, the ground layers 506a and 506b overlap with the signal line 504 in the lamination direction. In this regard, however, in the flexible substrate 500, in the cross-section structure diagram illustrated in FIG. 5B, the ground layers 506a and 506b do not overlap with the signal line 504 in the lamination direction. Namely, opening portions 508a and 508b are provided in the ground layers 506a and 506b, respectively.
Such a flexible substrate 500 as described above is easy to inflect and use, as described below. More specifically, since the ground layers 506a and 506b are configured using metal foil or the like, it is hard for the ground layers 506a and 506b to expand and contract compared with the insulation layers 502a to 502d. Therefore, as illustrated in FIG. 5B, in the flexible substrate 500, the opening portions 508a and 508b are provided in the ground layers 506a and 506b. Accordingly, in a portion illustrated in FIG. 5B, since the widths of the ground layers 506a and 506b become small, it is easy for the ground layers 506a and 506b to expand and contract. As a result, it is possible to easily bend the flexible substrate 500.
However, the flexible substrate 500 has a problem that unnecessary radiation from the signal line 504 occurs. More specifically, the opening portions 508a and 508b are provided in the ground layers 506a and 506b. Therefore, in a planar view seen from a lamination direction, the signal line 504 is exposed through the opening portions 508a and 508b. As a result, unnecessary radiation that is fundamentally absorbed by the ground layers 506a and 506b leaks to the outside of the flexible substrate 500 through the opening portions 508a and 508b. 